In cryptography, a block cipher may be a symmetric key cipher which operates on fixed-length groups of bits referred to as “blocks.” For example, during encryption, a block cipher may take a 128-bit block of plaintext as input and output a corresponding 128-bit block of ciphertext in accordance with a secret key. For decryption, the 128-bit block of ciphertext and the secret key may be used to determine the original 128-bit block of plaintext.
Galois Counter Mode (GCM) is a mode of operation for symmetric key cryptographic block ciphers. Generally, GCM is defined for block ciphers with a block size of 128 bits. GCM may involve two operations. First, the output of a block cipher may be multiplied by a hash key in a finite field. Second, the multiplication result may be reduced in size.
One current software-based GCM technique may utilize table lookups. However, building and storing of the tables may be time-consuming and resource intensive. For example, the tables may not readily fit into a level 1 (L1) cache of a processor and may require access to memory off chip, which in turn introduces latency. Other approaches may utilize a hardware-based technique, for example, found in cryptographic processors, which perform the reduction using a tree of exclusive-OR (XOR) gates specific to the polynomial of the finite field. This approach is field specific and cost-prohibitive for some implementations.
Accordingly, current techniques for performing computations associated with GCM may be time-consuming and/or cost-prohibitive.